The present invention relates to a sensor mat to be introduced into a vehicle seat, in particular a foil style sensor mat.
Function elements in foil style, such as membrane switches, foil pressure switches or similar elements, in general comprise at least two essentially elastic foil layers positioned at a certain distance from one another. This is effected, for example, by means of a spacer which is arranged around the active region of the function element and to which the two foil layers are glued with their respective edges. In the active region of the function element, various contact arrays are attached on the foil layers. When the two foil layers are compressed, an electric contact is created between these arrays, so that the switch element is operated. When the pressure is released from the foil layers, these in turn are, due to their elasticity, restored to their spaced position and the electric contact between the various contact arrays is interrupted again.
In order to guarantee a strong probability of response for such function elements with quite various ambient pressures, the function elements in general also comprise ventilating ducts, which connect the space between the two foil layers with the surroundings and thus enable a pressure compensation between the surroundings and the space. Such a function element is for example described in U.S. Pat. No. 4,314,227, which relates to a foil pressure sensor with a pressure-depending resistor.
A foil style sensor mat comprises a plurality of such function elements which are distributed across a certain area. Thus, the function elements form the active regions of the sensor mat. They are interconnected by elastic connection lines, in which moreover the electric bonding of the function elements extends. The elastic connection lines are formed by the foil layers laminated together by means of the spacer and are manufactured by punching areas without function elements from a plane layer construction.
In such a sensor mat, too, there are ventilating ducts which connect the spaces created between the two carrier foils in the region of the function elements with the surroundings. The ventilating ducts in this case often interconnect each a plurality of function elements or active regions of the sensor mat, respectively, where they extend in the flexible connection lines and at one side end at the surface of the layer construction. In order to avoid the penetration of water into the active regions of the sensor mat, the ends of the ventilating ducts are generally covered by an air permeable, but waterproof material. Such water barriers are known as microfibre fabric under trade names, such as Gore Tex(copyright).
As a sensor mat generally comprises a plurality of ventilating ducts (e.g. 30 to 40) which all end at various portions in the surface of the layer construction, accordingly, in the known sensor mats a corresponding number of microfibre patches have to be attached and fixed to the sensor mat. However, in view of the fact that the microfibre fabrics to be considered are relatively expensive compared to the other materials used in the sensor production, this means a not negligible increase in the production costs of such a sensor. Moreover, the gluing of the microfibre patches is relatively time consuming and represents an additional potential source of manufacturing defects.
Consequently, it is the object of the present invention to propose a simplified sensor mat for a vehicle seat.
According to the invention, this object is achieved by a foil style sensor mat, comprising a plurality of active regions interconnected by flexible connection lines and a flexible protective covering of a waterproof material. In this sensor mat, the protective covering can surround the whole sensor mat or completely surround only the connection lines of the sensor mat.
As the whole sensor mat or the flexible connection lines of the sensor mat, respectively, is surrounded by a protective covering, with the present sensor mat the attachment of a plurality of relatively expensive patches of microfibre fabrics to the individual ends of the ventilating ducts can be dispensed with. Thereby, the manufacture of the sensor mat is on the one hand, simplified, on the other hand, the production costs for the mat are reduced. In the present sensor mat, the waterproof material can, for example, comprise an inexpensive plastic foil, e.g. a PE-foil, into which the sensor mat or the connection lines of the sensor mat, respectively, are welded.
Another advantage of such a protective covering is the smooth surface of a plastic foil. Due to this smooth surface, the creaking sound between the sensor mat and a seat foam or a seat cover of a vehicle seat are considerably reduced. The pressure compensation between the individual active regions and the surroundings is e.g. effected within the protective covering with the sensor mat according to the invention. For this reason, the protective covering preferably comprises a compensating container 38 (shown in FIGS. 1 and 2) which is in fluid connection with the protective covering. The compensating container 3 can for example be connected in one piece with the protective covering, optionally via an extended connection duct 40 (shown in FIGS. 1 and 2). In this case, the compensating container can be advantageously positioned in a region of the seat outside the seating surface of the seat when the sensor mat is introduced into a vehicle seat.
In an advantageous embodiment, the protective covering comprises at least one vent opening, which is covered by means of a gas permeable but waterproof material. In this embodiment a pressure compensation can also be effected between the protective covering and the surroundings. The vent opening is preferably arranged in a region of the protective covering which will be outside the seating surface of the seat when the sensor mat is introduced into a vehicle seat. This ensures that the vent opening is not conglutinated when the sensor mat is glued to the seat foam. Moreover, by doing so, a load on the vent opening, for example covered by means of a microfibre patch, due to a passenger sifting on the seat can be effectively avoided.
The protective covering preferably comprises one or more fixing straps which are for example arranged at an outer edge of the protective covering. These fixing straps can be advantageously used for fixing the sensor mat e.g. at the seat foam or the seat substructure when the sensor mats are introduced into a vehicle seat. This can be effected by binding the fixing straps or by gluing, clamping or similar processes.
In an advantageous embodiment, the protective covering forms connection webs between various flexible connection lines. Thereby the number of connection lines at the actual sensor mat can be reduced as the necessary connection function is taken over by the protective covering. Thereby, the punching tools for punching the sensor mat are simplified and the tool length is reduced. Accordingly, the punching of the sensor mat can be effected with smaller punching forces and the blanking presses can have correspondingly smaller dimensions. As the connection webs of the protective covering are produced by thermal welding of a plastic foil, forces are not relevant in this process.
In a further advantageous embodiment, the protective covering surrounds the sensor mat with a certain clearance, i.e. the sensor mat has a certain mobility inside the protective covering. This is particularly advantageous if the sensor mat is to be glued onto a vehicle seat or if another function element, such as a seat heater, is to be glued onto the sensor mat. With conventional sensor mats which are glued to such a sandwich, distortions can be caused for example by thermal fluctuations, which distortions result in preloads of the active regions and thus adversely affect the response characteristic of the sensor mat. With the present design, the sensor mat has a certain mobility within the protective covering even after being glued, so that no preloads can develop any longer.
It should be noted that the protective covering can comprise a metallized foil and/or a UV-proof foil.